This invention relates generally to apparatus and methods for testing characteristics of a substance and more particularly, but not by way of limitation, to apparatus and methods for measuring the consistency and static gel strength of a cement slurry.
In the oil and gas industry, different fluids are used for various purposes in drilling and completing a well. For example, batches of cement must be made and pumped into the well for cementing the casing into the well bore. The cement is generally pumped through the casing for flow back up the annulus between the well casing and the well bore to create the necessary bond.
Because different batches of fluids can have different characteristics which affect how the fluids perform in the high temperature and high pressure environments found downhole, there is the need for equipment which can perform different tests on a fluid sample prior to the fluid being pumped downhole so that one can determine if that particular batch of fluid has the proper characteristics for the particular situation. For example, with respect to a cement slurry, the consistency and static gel strength of a particular blend are important characteristics to know. The consistency is important because it indicates the flowability of the cement slurry. The static gel strength is important because it relates to the ability of the cement to prevent gas leaks when the cement is flowed into the annulus. If the cement will not properly gel, gas may create channels through the cement to the surface causing a hazardous situation. The static gel strength also relates to the ability of the cement to flow, which indicates how long the cement slurry can be pumped.
The importance of obtaining the aforementioned two characteristics of a cement slurry are well known in the art. Various types of single-function test apparatus by which one or the other of the aforementioned characteristics can be measured are known. Multi-function apparatus have also been proposed or developed wherein separate drive equipment and often separate displays are used for separately operating on a container holding the substance to be tested. However, we are not aware of a single, compact apparatus by which both consistency and static gel strength can be measured utilizing one and only one drive element so that the apparatus can be constructed more compactly and cost effectively. To further enhance the compactness and cost effectiveness of such a needed apparatus, such apparatus should include a single display and means by which either one or the other of the tested characteristics can be displayed since only one test would be conducted at any one time, thereby obviating the need for duplicate displays. Of course, such an apparatus should also have the heating and pressurizing abilities of known types of test equipment. It is also desirable that such an apparatus should have the capability of being controlled by a suitable computer, such as a microprocessor-based device. A corresponding novel method of efficiently testing a substance for these characteristics is also needed.